Cyanohydrins are important starting materials which can be used to synthesize precursors for insecticidally active compounds.
For example, 2-hydroxy-3-methylbutyronitrile, can be used as the starting material in the synthesis of 2-methyl-3-cyano-3-(ethylpropylthiophosphoryloxy)propane, an extremely active insecticide.
The procedure for the preparation of cyanohydrins calls for the addition of hydrogen cyanide to carbonyl compounds as follows: ##STR1## wherein R can be hydrogen, alkyl, haloalkyl, alkoxyalkyl, aryl, alkylaryl, haloaryl, or alkoxyaryl.
The reaction is generally accomplished by reacting the carbonyl compound with liquid hydrogen cyanide in the presence of a basic catalyst as set forth in British Pat. Nos. 416,007 and 452,285; and French Pat. Nos. 804,124 and 812,366. The reaction is reversible and the cyanohydrin product is usually stabilized by acidification before isolation.
In U.S. Pat. No. 2,731,490, a continuous method for the production of cyanohydrins by passing gaseous hydrogen cyanide to a mixture of an aldehyde or ketone and an aqueous alkali solution followed by adjusting the mixture's pH to 7 is described. Other similar production methods employing gaseous hydrogen cyanide as starting reactant are described in U.S. Pat. Nos. 2,175,805 and 2,794,042.
A more convenient method to prepare cyanohydrins is to generate hydrogen cyanide in the reaction mixture by the action of sulfuric, nitric, phosphoric, or acetic acid on an alkali cyanide in the presence of a carbonyl compound as set forth for example in Organic Synthesis, Coll. Vol. II, 7 (1941); Lucas and Prater, J. Am. Chem. Soc., 59, 1682 (1937); Colonge and Joly, Ann. Chim., (11) 18, 303 (1943); Ultee, Rec. Trav. Chim., 28, 1, 248 (1909); and Boekelheide and Schilling, J. Am. Chem. Soc., 72, 712 (1950).
Alternatively, as set forth in Organic Syntheses, Volume 20, 43 (1940), an alkali bisulfite can also be employed to react with a carbonyl compound to form a bisulfite addition product, which is then reacted with alkali cyanide to form the desired cyanohydrin. ##STR2##
Although these conventional methods are effective, they only afford moderate yields of reaction products. Furthermore, the cyanohydrin products obtained from the above prior art procedures require additional purification steps in order to realize a commercially acceptable quality product. For example, as described in Organic Synthesis, Collective Volume II (page 7) supra, the synthesis of acetone cyanohydrin from acetone, sodium cyanide, and diluted sulfuric acid afforded only 77-78% yield of product which had to purified by vacuum distillation.
Consequently, there exists a need for a more efficient and economical process for the production of cyanohydrins.